1. Field of the Invention
The present invention relates to a battery charging device for a vehicle which provides a signal representing battery charging condition and is controllable at any time from the outside.
2. Description of Related Art
Recently, the battery charging device is required to serve various purposes such as reduction in the fuel consumption, the active shock absorbing, improvement in the vehicle drive performance, reduction in the engine idling speed and high power devices including an electrically heated catalyst (EHC) unit. As a result, the battery charging device is required not only to maintain the battery charging voltage at a desired level but also to change the generator condition according to load conditions and vehicle running conditions. For this purpose, it is necessary to provide signals representing generator conditions in real time.
Such generator conditions include the generator output signals such as output current, output power, field current, duty ratio of a field current control transistor or the like, generator output power such as battery charging voltage, battery voltage and stator phase voltage and temperature of the generator. The above conditions are detected by the amount representing the generator conditions, changes in the amount indexes and/or the like. The generator is controlled to change the amount of the generator conditions and/or changes in the amount, or by limiting or by restricting maximum or minimum indexes of the generator conditions within designated values.
For example, when temperature of the engine is lower than a designated value and the engine operation is unstable, the generator output power or torque is controlled to be low to prevent the engine from stalling. When temperature of the generator is higher than a designated temperature, the generator output is controlled to prevent further temperature rise. The above control is carried out by an outside ECU (electronic control unit) which controls a switching transistor to change the duty ratio of the field exciting current.
In order to provide the outside control and monitoring by the ECU, a wired signal carrying system has been proposed. Such system includes a generation control signal transmitting wire which transmits generation control signals from an outside ECU to a voltage regulator of the generator and a generator condition signal transmitting wire.
However, the above wired signal transmitting system has the following problem.
That is, the two transmitting wires makes the vehicle wire harness bulky and heavier and increase the number of connector terminals and connector size, resulting in increase of the regulator size which causes difficulty of the installation thereof and in the production cost thereof. The increase of the number of wires increases the possibility of disconnection of the transmitting wires or of contacting with the body earth or battery due to vehicle vibration, resulting in erroneous operation of the battery charging system. The increase of the connector terminals also increases possibility of subjecting themselves to the electrostatic surge voltage generated by the human body at installation work.
When the above transmitting wires are disposed in the device as a band cable or parallel cables, the cross talk increases and SN ratio decreases. Further, since the electro-magnetic noise in the engine room is significant, it may cause erroneous operation or detection if the electro-magnetic noise overlaps the cross talk.